1. Field of the Invention
The present invention relates to a polyorganosiloxane graft copolymer excellent in impact resistance, low-temperature characteristics and weather resistance, and further giving molded products excellent in bond strength to paint film applied thereon.
2. Description of the Related Art
As thermoplastic resins excellent in impact resistance, low-temperature characteristics and weather resistance, a polyorganosiloxane graft copolymer obtained by graft-polymerizing a monomer having an ethylenically unsaturated bond (e.g. acrylonitrile, styrene) onto polyorganosiloxane rubber is disclosed in Japanese Patent Application Kokai No. 61-106614. Also, a graft copolymer obtained by graft-polymerizing particular amounts of an epoxy group-containing vinyl monomer and other vinyl monomer onto a polyorganosiloxane polymer copolymerized with a graft-linking agent as copolymer component is disclosed in Japanese Patent Application Kokai No. 2-138360.
However, the former graft copolymer disclosed in Japanese Patent Application Kokai No. 61-106614 has problems although it is excellent in impact resistance, low-temperature characteristics and weather resistance. Firstly, in the course of production of the graft copolymer, an organosiloxane oligomer which is very difficult to remove from the graft copolymer is produced as by-product. Secondly, when the graft copolymer is molded, this oligomer blooms out to the surface of the molded product, so that when the molded product is painted, the bond strength of the paint film is low. Similarly, the graft copolymer disclosed in Japanese Patent Application Kokai No. 2-138360 also has problems although it is excellent in impact resistance, low-temperature characteristics and weather resistance. That is, the adhesion property of paint film applied to the molded product of this graft copolymer is not of very high level, and besides the above adhesion property becomes quite poor as the amount of the polyorganosiloxane polymer in the graft copolymer becomes large. This graft copolymer further has a problem that when it is put in wet heat conditions under pressure, its impact strength becomes remarkably poor.